The present invention relates to techniques for use in interbody fusion procedures, instruments for performing such procedures, and implants insertable in the spinal disc space. More specifically, but not exclusively, the present invention relates to implants, methods and instruments for use in a posterior lateral approach to the disc space, such as a transforaminal approach.
Normally intervertebral discs, which are located between endplates of adjacent vertebrae, stabilize the spine and distribute forces between the vertebrae and cushion vertebral bodies. The spinal discs may be displaced or damaged due to trauma, disease or aging. A herniated or ruptured annulus fibrosis may result in nerve damage, pain, numbness, muscle weakness, and even paralysis. Furthermore, as a result of the normal aging processes, discs dehydrate and harden, thereby reducing the disc space height and producing instability of the spine and decreased mobility. Most typically surgical correction of a collapsed disc space includes a discectomy (surgical removal of a portion or the entire intervertebral disc). The discectomy is often followed by restoration of normal disc space height and bony fusion of the adjacent vertebrae to maintain the disc space height.
Access to a damaged disc space may be accomplished from several approaches to the spine. One approach is to gain access to the anterior portion of the spine through a patient""s abdomen. However, extensive vessel retraction is often required and many vertebral levels are not readily accessible from this approach. A posterior approach may also be utilized. However, this typically requires that both sides of the disc space on either side of the spinal cord be surgically exposed. This may require a substantial incision or multiple access locations, as well as extensive retraction of the spinal cord. To alleviate problems associated with both anterior and posterior approaches to the spine, a posterior lateral approach, such as a transforaminal approach, to the disc space may be utilized. While it is desirable to place one or more implants in the disc space so that the load of the spinal column is evenly distributed, accurate placement of implants in the disc space from a single posterior lateral approach has heretofore been extremely difficult. Thus, this approach to the spine is seldom used in practice.
Therefore, there remains a need for improved instruments, implants and techniques for use in a posterior lateral approach to the disc space that allows unilateral disc space preparation and implant insertion to provide bilateral stability to the subject disc space.
The present invention provides implants, instruments and methods particularly adapted for unilateral disc space preparation and implant insertion from a posterior lateral approach to the disc space, such as is provided with a transforaminal approach.
In one aspect a lamina spreader is provided. The lamina spreader has arms pivotally connected with one another. The arms each include a lamina engaging portion at the distal end of the arm. In a preferred form, the arms are hinged so that the proximal ends of the arms can be rotated out of the operative field while the spreader is engaged to the lamina.
In another aspect, a disc space spreader is provided. The spreader has a pair of branches pivotally connected to one another. The branches have a spreading portion attached to the distal end of each arm. Each arm includes a lateral offset extending between the spreading portion and the articulating arm. A spreading mechanism is provided to assist in separating the spreading portions. In a further form, a pusher is provided to assist the surgeon in inserting the spreading portions into the disc space.
In further aspect of the invention, rotatable distractors are provided with distractor heads configured for insertion into the disc space via a unilateral approach. A lever arm can be secured to the distractor shaft to assist in rotation of the distractor.
In still a further aspect of the invention, cutting tools for unilateral disc space preparation are provided. Cutting instruments according to the present invention preferably have a longitudinal shaft with a cutting blade disposed at the distal end of the shaft. The cutting instruments include straight and curved reamers, cutting blades that are movable along or around a guide shaft, pull scrapers and push scrapers, straight chisels, and curved chisels movable along a guide shaft.
In yet another aspect, the present invention provides improved devices for implant insertion. An implant template is provided for the surgeon to determine the required implant size. Implant insertion devices according to the present invention comprise a shaft having a longitudinal axis and an implant connector at the distal end of the shaft. The shafts can be straight, curved, or flexible. In one form, the distal end of the shaft includes a bend for implant insertion to the distal portion of the disc space. In another form, the inserter shaft has a lateral offset. According to a further aspect of the invention, a pusher is provided and useable with the inserter to facilitate implant placement in the disc space.
In still a further aspect, the present invention provides methods for disc space preparation and implant insertion from a unilateral transforaminal approach to the spine. The method contemplates accessing the disc space and providing a posterior lateral opening into the disc space. The lamina can be spread to facilitate access. The disc space is then distracted with disc space spreaders. Cutting instruments are inserted through the opening to remove disc material and bony material from the endplates to prepared the disc space for implant insertion. The implant is then inserted through the opening and into the distal portion of the disc space. In one form, the unilateral approach utilizes at least two bilaterally positioned implants, with one of the implants in the distal portion of the disc space. In a second form, a single implant laterally spanning the disc space is positioned through the opening.
Further aspects, forms, embodiments, objects, features, benefits, aspects and advantages of the present invention shall become apparent from the detailed drawings and descriptions provided herein.